Mobile operators of wireless telecommunications networks frequently use Wi-Fi networks to offload data traffic from the wireless telecommunications networks. The usage of Wi-Fi networks is motivated mainly because of its free and wide unlicensed spectrum, as well as, the increased availability of Wi-Fi capabilities in wireless devices, such as, e.g. smartphones and tablets. The end-users of the wireless devices are also becoming more and more comfortable with using Wi-Fi networks.
In many instances, more than one Radio Access Technology (RAT) may be used simultaneously by the same User Equipment (UE). This may be to improve performance, for example, by increased throughput, improved resiliency and/or improved coverage. Typically, Multi-Path TCP (MPTCP) can be used to transfer TCP segments belonging to a single end user application using multiple paths (“subflows”) to and from the client. One very likely scenario is that one MPTCP subflow goes over Wi-Fi/WLAN and another MPTCP subflow goes over a 3GPP RAT.
Alternatively, a second RAT may be used as a backup connection for a main connection using a different access network. With MPTCP, it is also possible to define paths as backup paths, which are only to be used when there are no other available regular paths. It is envisaged that a common scenario in the future of MPTCP is that smart phone users are having a regular path or subflow towards a home Wi-Fi access point and a backup path or subflow using a 3GPP operator subscription, for example, over WCDMA or LTE radio access network.
However, there are drawbacks to establishing and maintaining such backup paths. These are typically used to transmit only control signalling to maintain the backup path/subflow, for example establishment, release and possible keep-alive signalling for the backup path/subflow, and are only occasionally associated with data traffic. It is necessary to create both radio access network and core network level of connectivity to enable such establishment and release of backup paths. One example is in relation to 3GPP Evolved Packet System consisting of both LTE (E-UTRAN) radio access network and EPC core network: A UE that wants to establish a backup path, e.g. using MPTCP, needs to enter a so called “connected” state to enable communication towards an MPTCP-server via the EPS. The UE is normally in the “connected” state for a short while and then moves to an “idle” state. Once the backup path is to be released, the UE needs to again enter the “connected” state to signal the release of the backup path. Therefore, a lot of signalling overhead may be introduced without any useful information being sent, resulting in additional load on different network nodes and increased interference on other signals. In some situations, for example, when there is high load on a network, it may be desirable to limit the backup paths that do not carry any traffic, for example by restricting their usage of network resources via connection admission control, by giving such paths a lower priority compared to other paths and UEs, or by restricting their power.
In order to implement such restrictions, it is necessary for the networks to recognise which paths are backup paths. It is also beneficial to recognise that a UE has only backup paths in a particular radio access network. Two mechanisms exist in the prior art for identifying backup paths. The first of these is the use of the “B” bit in the MPTCP header and signalling. The second is the use of deep packet inspection in the network to identify paths in which little or no data is being transmitted. Both of these mechanisms require both a radio level connection (and also a core network level connectivity) and a backup path to be already set up before identification of the backup path can take place, with a consequent lack of the option of introducing the described restrictions early on as part of the establishment of the radio level connection.